Nonaqueous electrolyte batteries which are charged and discharged based on the movement of lithium ions between a negative electrode and a positive electrode are being extensively investigated and developed as batteries having a high energy density.
In addition to use as small power sources for electronic devices, the nonaqueous electrolyte batteries are expected to be used as medium and large power sources, as well. Lifetime properties and high stability are required for the use of the batteries as medium and large power sources.
As a positive electrode active material for nonaqueous electrolyte batteries, for example, a lithium-transition metal composite oxide is used. For example, Co, Mn or Ni is used as a transition metal. In recent years, spinel type lithium manganese and olivine type compounds such as an olivine type lithium iron phosphate and an olivine type manganese lithium phosphate have been actively researched as a low-cost and safe positive electrode material.
A carbon material is commonly used as a negative electrode material. However, from the viewpoint of lifetime properties and safety, attention is focused on a nonaqueous electrolyte battery manufactured using a titanium oxide material, which has a Li inserting and extracting potential higher than that of a carbon material. Particularly, a spinel type lithium titanium oxide is known as a zero-strain material which does not undergo volume expansion and shrinkage during Li inserting and extracting reactions. Accordingly, a nonaqueous electrolyte battery manufactured using the spinel type lithium titanium oxide is excellent in lifetime properties and safety properties. Further, the nonaqueous electrolyte battery manufactured by using the spinel type lithium titanium oxide is also excellent in rapid charge performance. However, the theoretical capacity per weight of the spinel type lithium titanium oxide is 170 mAh/g, which is lower than that of the carbon material.
Consequently, titanium oxide material having a higher capacity is anticipated. Recently, attention is focused on a titanium and niobium-containing compound TiNb2O7, whose theoretical capacity is 387 mAh/g, as a high capacity titanium oxide material.